1. Field of the Invention:
This invention relates to a printed circuit board for mounting circuit elements to form an electric circuit thereon.
2. Description of the Prior Art:
It has been proposed to provide a hybrid integrated circuit for minimizing an electric circuit and for more effectively producing an electric circuit. Such a hybrid integrated circuit is obtained by temporarily mounting chip-shaped leadless elements on the board through adhesive resin and then electrically connecting the electrodes of the leadless elements with the lands of the printed circuit board through a solder dipping operation. On this solder dipping operation, solder flux is evaporated, and flux gas is generated. During the solder dipping operation for areas with leads, the evaporated gas escapes upwardly through piercing holes formed in the circuit board for the insertion of the lead wires, and hence the gas is not trapped in the dipping position. However, in the solder dipping operation for leadless elements, the gas has no escape and stays in the shade of the elements, because piercing holes are not formed on the portions where leadless elements are to be mounted. Further, the air staying near the elements has its escape cut off. The evaporated gas or the air acts to prevent melted solder from extending into the surface of the electrodes. Accordingly, the electrodes of the leadless elements are not connected to the lands of the circuit board with certainty. When mounting density of the elements is high or many leadless elements are closely mounted on the board substrate, the above mentioned problem is serious. To solve the above mentioned problem, it has been proposed to form piercing holes on the lands or areas intended for a leadless element, or near the lands to permit the escape of the gas or the air. However, this proposed method increases the number of the process for manufacturing the printed circuit board, and still more the method requires additional dies for piercing holes or increases the cost of the existing dies.